1. Field of the Invention
The present invention relates to technology in an image forming apparatus, such as a printer or a copier, for determining the mounted state of an image forming unit that can be removed from the image forming apparatus.
2. Description of the Related Art
In image forming apparatuses, normal printing cannot be performed if the cartridge (the image forming unit) that is to perform image formation is not mounted properly. The image forming apparatus therefore carries out a cartridge mounted state determination. If this determination is carried out using mechanical parts such as switches and actuators, the number of parts increases, and the size of the image forming apparatus increases due to the need to ensure space for such parts. For this reason, Japanese Patent Publication No. 7-60288 discloses a configuration in which the cartridge mounted state determination is carried out using transfer current flowing in a transfer roller due to the transfer roller outputting a transfer bias to a photosensitive member of a cartridge. Also, Japanese Patent Laid-Open No. 6-3891 discloses a configuration in which the cartridge mounted state determination is carried out using charging current flowing in the charging roller due to the charging roller outputting a charging bias to a photosensitive member.
Recent years have seen progress in the reduction of the cost of image forming apparatuses, and a configuration has been used in which the power supply unit that supplies a voltage to an output member that outputs a bias to a photosensitive member of a cartridge is used in common by each cartridge. In an image forming apparatus in which the power supply unit is used in common by multiple cartridges, when a voltage is applied by the power supply unit, current will flow to each of the cartridges. It is therefore possible to specify the number of cartridges that are not mounted based on the current value, but it is not possible to specify which cartridges are not mounted. Also, with a configuration in which the mounted state is determined by the power supply unit applying a voltage to only specific cartridges in order, a circuit is needed in order to switch the voltage application, and the determination becomes time-consuming due to the time needed to switch the voltage application destination and the like.